dsm
Damn simple finite state machine
About
DSM is a observable simple finite state machine implementation for Python. Transitions may be programmed declaratively or imperatively. Inputs and state changes are emitting observable events.
Requirements
- Python 2.7, 3.5, 3.6
observable-
sixfor compatibility between Python 2 and Python 3
Installation
pip install dsm
Usage
Django integration
It is possible to integrate dsm with Django models by
declaring a StateMachineField.
from django.db import models
from dsm.fields import StateMachineField
class Order(models.Model):
status = StateMachineField(
transitions=(
('new', ['confirmed'], 'processing'),
('processing', ['cancel'], 'cancelled'),
('processing', ['send'], 'sending'),
('sending', ['deliver'], 'finished'),
),
max_length=16,
choices=(
('new', _('New')),
('processing', _('Processing')),
('sending', _('Sending')),
('finished', _('Finished')),
('canceled', _('Cancelled')),
),
db_index=True,
default='new'
)Now you can create an Order and check it's status:
>>> order = Order.objects.create()
>>> order.status
new
>>> type(order.status)
dsm.fields.MachineStateThe string representation of status field is same as state name
provided in transitions declaration, but internally there is always
dsm.fields.MachineState instance.
Declarative
FSM declaration:
import string
import dsm
class SumatorMachine(dsm.StateMachine):
class Meta:
initial = 'init'
transitions = (
('init', list(string.digits), 'digit_enter'),
('digit_enter', list(string.digits), 'digit_enter'),
('digit_enter', '=', 'summarize'),
)Usage:
Initialization:
fsm = SumatorMachine()Processing one value:
fsm.process(value)Processing multiple values:
fsm.process_many(iterable)Gathering the current state:
>>> fsm.state
'summarize'Resetting to the intial state:
fsm.reset()Listening on events:
fsm.when('state', func)Events example:
>>> the_sum = 0
>>> def add_digit(x): global the_sum; the_sum += int(x)
>>> def reset(x): global the_sum; the_sum = 0
>>> fsm = SumatorMachine()
>>> fsm.when('digit_enter', add_digit)
>>> fsm.when('init', reset)
>>> fsm.process_many('666=')
'summarize'
>>> the_sum
18Events example (class based):
>>> class Sumator(object):
... def __init__(self):
... self.total = 0
... self.fsm = SumatorMachine()
... self.fsm.when('digit_enter', self.add)
... self.fsm.when('init', self.reset)
...
... def add(self, x):
... self.total += int(x)
...
... def reset(self, x):
... self.total = 0
...
... def summarize(self, values):
... self.fsm.reset()
... self.fsm.process_many(values+'=')
... return self.total
>>> s = Sumator()
>>> s.summarize('666')
18Imperative
import string
import dsm
fsm = dsm.StateMachine(
initial='init',
transitions=dsm.Transitions((
('init', list(string.digits), 'digit_enter'),
('digit_enter', list(string.digits), 'digit_enter'),
('digit_enter', '=', 'summarize'),
))
)License
BSD
